1. Field of the Invention
The present invention relates to rotary fluid handling devices and, in particular, rotary air motors of the type having a rotor rotating in a chamber with vanes slidably mounted in the rotor so that the ends of the vanes constantly engage the walls of the chamber as the rotor rotates.
2. Description of the Prior Art
Current air motors typically have a rotor which rotates within a stator chamber. The rotor has slots in which vanes are slidably disposed. The rotor may have either radially arranged vanes ("RAV") or tangentially arranged vanes ("TAV"). In either type, the motor typically has a pair of end plates which respectively close the opposite ends of the stator chamber and which are respectively spaced a clearance distance from the adjacent ends of the rotor and the vanes to accommodate free rotation thereof.
In the RAV type motor, the vanes are in the form of substantially flat plates which are respectively slidably received in radial slots in the rotor for sliding radial movement between innermost and outermost positions. Typically, the vane slots extend into the rotor shaft or hub and the vanes have a radial extent substantially equal to that of the slots. As the rotor rotates, the vanes are urged radially outwardly by centrifugal force into sliding engagement with the inner surface of the stator. Typically, the rotor is mounted eccentrically with respect to the stator chamber so that as it rotates the vanes move radially in and out between their innermost and outermost positions during each rotation.
The TAV type air motor is substantially the same as the RAV type motor, except that the vanes are respectively disposed in slots which are arranged substantially tangentially with respect to the rotor shaft rather than radially.
RAV type motors are characterized in that: (1) the motor may be bi-directional, i.e., since the vanes engage the stator chamber wall substantially radially, they exhibit substantially the same drag in either direction of rotation; (2) a larger number of vanes can be accommodated in the motor and (3) full sealing effectiveness is achieved against the inner wall of the stator because of the centrifugal forces on the vanes. The TAV type air motor is characterized by: (1) a greater vane length which permits increased wear life; (2) the accommodation of a through shaft for the rotor, since the vanes do not extend inwardly of the shaft circumference; (3) unidirectionality, since the vanes will tend to jam against the wall of the stator if the rotor is rotated in the same direction that the vanes exit the rotor; and (4) a performance drop because the vanes engage the stator chamber along a line which is inclined with respect to the direction of the centrifugal forces, thereby reducing the sealing effect.
In both the RAV and TAV motors, when the vanes are in their outermost positions, their inner ends are typically spaced radially outwardly from the hub or shaft of the rotor, creating a leakage gap in the region between the end plates and the end faces of the rotor. This leakage could be alleviated in the case of the TAV air motor if the vanes and slots are sufficiently long that the vane will remain tangent to the rotor shaft in all positions of the vane, but this reduces the number of vanes which can be accommodated in a rotor.
Accordingly, in prior air motors it is typically necessary to provide for a minimal clearance between the end plates and the adjacent ends of the rotor in order to avoid excessive leakage between the compartments formed by adjacent vanes. This necessitates the use of expensive precision parts made to very close tolerances.
Referring to FIGS. 1 and 2, there is illustrated a prior art air motor 10 which includes a stator 11 having a cylindrical inner surface 12 defining a cylindrical chamber 13. A cylindrical rotor 15 is rotatably mounted in the chamber 13 on hub structure 16 which includes a shaft 17 extending axially of the rotor 15, the hub structure 16 having an outer surface 18. Formed in the rotor 15 are four equiangularly spaced apart radial slots 19, each extending from the outer surface of the rotor 15 radially into the shaft 17. Four vanes 20 are respectively slidably disposed in the slots 19. Each of the vanes 20 is in the form of a flat plate extending the length of the rotor 15 and having a width substantially equal to the depth of the slots 19. Each of the vanes 20 has radially spaced outer and inner edges 21 and 22 and a pair of axially spaced end edges 23 (one shown in FIG. 2). In operation, as the rotor 15 rotates, the vanes 20 are urged by centrifugal force radially outwardly to hold the radially outer edges 21 thereof in sliding engagement with the inner surface 12 of the stator 11 for cooperation therewith and with the outer surface of the rotor 15 to divide the chamber 13 into four compartments 24.
The air motor 10 also includes a pair of end plates 25 (one shown), each having an inner surface 26 which bears against the associated end face of the stator 11 and is spaced a small clearance distance from the adjacent end edges 23 of the vanes 20 and the adjacent end face 27 of the rotor 15 so as to provide a running clearance. For purposes of illustration, the clearance gap between the end plate 25 and the vanes 20 is illustrated as being a very slight gap, while the clearance gap between the end plate 25 and the rotor 15 is more substantial, and greatly exaggerated. The difference is intended to be the difference between a very close tolerance, e.g., a few thousandths of an inch and a loose tolerance, e.g., a few tens of thousandths of an inch. The clearance between the end plate 25 and the vanes 20 may be substantially the same as that between the end plate 25 and the rotor 15, but is shown as being different for purposes of illustration.
As can be seen, when the vanes 20 are in their outermost positions (the bottom vane as seen in FIGS. 1 and 2), the inner edge 22 of the vane is spaced radially outwardly beyond the outer surface 18 of the hub structure 16, creating a leakage gap 28 therebetween which permits leakage of air between the adjacent compartments 24 at the ends of the rotor 15. If the parts are made to loose tolerances, this leakage is substantial and seriously impairs the efficiency of the motor. Accordingly, prior art air motors have had to maintain the end clearance gap between the end plate and the adjacent ends of the vanes and rotor as small as possible, necessitating the manufacture of the parts to very close tolerances, at considerable expense.
In FIG. 3, there is illustrated another prior art air motor 30 which is similar to the air motor 10, except that it has tangential, rather than radial vanes. More specifically, the air motor 30 includes a rotor 35 which is rotatably mounted on hub structure 36 including an elongated shaft 37, the hub structure 36 having an outer surface 38. Formed in the rotor 35 are four equiangularly spaced apart slots 39, each extending tangent to the outer surface 38 of the hub structure 36 and having the inner end thereof terminating substantially at a diameter of the hub structure 36. Vanes 40 are respectively disposed in the slots 39 and have a width substantially equal to the depth of the slots 39, each of the vanes 40 having radially spaced outer and inner edges 41 and 42. The outer edge 41 is angled or curved to substantially match the curvature of the inner surface 12 of the stator so as to provide an effective seal, necessitating unidirectional operation. The vanes 40 serve to divide the chamber into four compartments 44.
As can be seen in FIG. 3, when the vanes 40 are in their innermost or fully retracted positions, they are tangent to the outer surface 38 of the hub structure 36 so as to provide a seal thereat between the adjacent compartments 44. However, when the vanes 40 are moved outwardly away from their fully retracted positions, a leakage gap 48 will be opened between the end plates and the adjacent ends of the rotor 35, in substantially the same manner as was described above in connection with FIGS. 1 and 2.